This disclosure relates to a method and system for feeding comminuted cellulosic fibrous material (“chips”) to a treatment vessel, such as a continuous digester, which may produce cellulosic pulp. This disclosure particularly relates to the mounting and support mechanism for adjusting and monitoring a rotary feeder.
Rotary feeders, for example high-pressure feeders (HPFs) and low-pressure feeders (LPFs), asthma feeders, and other similar devices, transfer chips from a chip supply system to a chip processing system, such as a continuous digester system for chemical pulping of wood chips or other cellulosic material. HPFs are described in U.S. Pat. No. 6,669,410 and transfer chips from a low-pressure chip supply system to a high-pressure chip supply system. Other rotary feeders such as LPFs transfer chips from atmospheric (or near atmospheric) pressure to a low-pressure chip supply system (such as 15 psig to 35 psig).
LPFs and HPFs are components of a continuous digester system. They provide the ability to change (increase) the pressure of the slurry of wood chips and liquor to be fed to the digester vessel. Without the high-pressure chip slurry provided by one or each of either of the LPF and HPF, the digester system is disabled. Other rotary feeders may also be used in other locations within a pulp mill to impact a change in pressure of the slurry material entering the rotary feeders versus the pressure of the slurry of material leaving the rotary feeders. When a rotary feeder is shut-down for repair or maintenance, the digesting process and the resultant production of pulp ceases until the rotary feeder is restarted.
Rotary feeders are conventionally mechanical rotary valve devices adjusted with manual or motor driven controls. A common control adjustment is to adjust the clearance between a rotating pocket rotor and a cylindrical chamber of the housing for a rotary feeder. The clearance is usually a gap between an outer cylindrical surface of the rotor and an inner cylindrical surface of the chamber. This clearance (gap) typically allows a small amount of liquid to serve as a lubricant between the pocket rotor and chamber. In this document, the terms “clearance” and “gap” are used taken to mean the same.
If the clearance is too wide, a pressure loss can occur in the rotary feeder fluid flowing through the rotary feeder, excessive liquid and cellulosic material may flow through the clearance (gap) and accumulate in the housing, e.g., in the end bells of the housing, and excessive liquid may leak through to a low-pressure outlet of the rotary feeder. If the clearance is too narrow, metal to metal contact may occur between the rotor and chamber and debris caught in the clearance (gap) may etch grooves in the rotor or chamber. Accordingly, the clearance between the pocket rotor and chamber should generally be maintained in an acceptable range. Support to prevent torsion and axial forces acting on the rotary feeder due to normal operation should generally be provided.
The clearance between the pocket rotor and chamber of the housing can be adjusted by moving the rotor axially with respect to the housing. The pocket rotor and chamber each are generally slightly tapered. Because of the taper, the clearance between the rotor and housing can be adjusted by axial movement of the rotor. Examples of a manual and motor driven controls are disclosed in EP 0732280-A1, a Bauer Rotary Valve Brochure published in 1969, Swedish Patent C503684, Great Britain Patent GB 503 710, German Patent DE 721 850, U.S. Pat. No. 4,372,338 and U.S. Pat. No. 7,350,674.
As described in these disclosures, axial movement of the rotor could be by manually turning a wheel at the end of a rotary feeder, or based on automatic computer control of a motor to impart axial movement of the rotor. In each of these disclosures the support mechanisms for the adjustment of the pocket rotor are located on the outside of the housing. Operator safety and adjustment mechanism accuracy concerns arise when the support mechanisms are located outside the housing.
Operation personnel or others in close proximity to the rotor housing could be injured when the axially moving gearbox is operated without warning. This situation creates a pinch point where persons could become injured. Another disadvantage of the support and control mechanisms being on the outside of the rotary housing is the accuracy of the adjustments made.
Because the gearbox for the adjusting mechanism slides on bolt heads, a less than precise adjustment is made. As the sliding area is exposed to the outside environment, dirt, grime, and elements of the weather can be deposited on the sliding area resulting in obstructions on the metal surface of sliding area. The obstructions on the metal surface can inhibit the smooth movement of the gearbox on the sliding area and increase the opportunity for personnel injury when trying to clean or remove obstructions. In addition, exposure to the environment increases the wear of the metal to metal surfaces of the support and control mechanism of prior art systems.
An example of a suitable automatic computer control method for the prior art systems currently in use can be found in US 2009-0142147 (incorporated here by reference).
Maintaining an optimal clearance between the pocket rotor and chamber of the housing can be helpful to extend the operational life of the rotary feeder, particularly the pocket rotor and surface of the chamber. Additionally, it is important to maintain an optimal clearance between the pocket rotor and chamber of the housing to avoid damage to the rotor and chamber, to minimize the power load of the rotary feeder, and to minimize the fluid pressure loss due to fluid leakage through the clearance between the pocket rotor and the chamber of the housing. There is a long felt need is to provide an effective and simple support mechanism (structural support) for the rotary feeder adjustment mechanism including the power source for the adjustment mechanism. Additionally, there is a long felt need to protect the adjustment mechanism of the rotary feeder from exposure to the environmental elements existing in the location of the rotary feeder.